As a candidate for nonvolatile memory applications of next generation, resistive random-access memory (RRAM) attracts abundant attention due to its simple metal-insulator-metal structure, excellent scalability, fast switching speed, low-voltage operation and good compatibility with CMOS technology. Two common resistance switch modes for resistive random-access memory include bipolar and unipolar operations.
However, bipolar operation may cause area consumption. Further, general resistive random-access memory includes planar MOS selectors which may also cause area consumption.
Therefore, the unipolar operation is more attractive since ideally 4F2 cell size can be integrated in one-diode-one-resistor (1D1R) array for high density application. Several kinds of unipolar RRAM materials, such as WOx, HfO2 and Ta2Ox, have been studied. The silicide based materials also catch the attention due to their great integration compatibility with CMOS technology.